What is the probability of a through-going San Andreas rupture? A definitive answer to this question has fundamental implications for forecasting the earthquake hazard in southern California. Related to the potential for earthquakes rupturing through the San Gorgonio Pass are other questions:

What is the subsurface geometry of active faulting through the San Gorgonio Pass? In order to best predict potential rupture through the San Gorgonio “knot” and ground motions we need to know the active fault configuration.

What is the earthquake potential in the San Gorgonio Pass region? If fault geometry, stressing rates and slip rates are known, then we will be able to develop more accurate earthquake models, which will in turn produce better estimates of earthquake size, earthquake interactions, ground motion, and seismic hazard.

We will hold a full-day workshop in conjunction with the 2014 SCEC Annual Meeting in Palm Springs. The workshop will kick off with a field trip to the northern Coachella Valley. The afternoon of the workshop will feature short presentations on recent findings for the SFSA from researchers from the geophysics, paleoseismology, geomorphology, geodesy, mechanical modeling and rupture modeling communities. Significant discussion time will focus on how we are addressing the three key questions for the San Gorgonio Pass SFSA, any obstacles to achieving the goals that were formulated in 2012 and fine-tuning the science plan. The results of this workshop and field trip will be renewed and optimized research goals and collaborations for the next year of the SFSA and beyond.

The field trip will take participants to the northern Coachella Valley, where the San Andreas fault splits to the north to the Mission Creek, the Garnet Hill and the Banning strands of the San Andreas fault. The subsurface geometry of the Garnet Hill and Banning strands were the topic of much discussion at the 2012 SGP Workshop. Micro seismicity provides some constraints into potential structure but alternative interpretations fit the data (Carena et al., 2004; Nicholson et al., 2013). Meanwhile crustal deformation models (Fattaruso et al., 2013 SCEC) show that the changes in fault geometry greatly affect deformation in the area where these faults branch so that resolving this uncertainty is a high priority of the San Gorgonio Pass SFSA. Much needed new strike-slip rates along the Garnet Hill fault may be available from new trench that is planned for January 2014. Visiting this site as well as a site with recent slip rates along the Banning strand will provide great settings for discussions of the roles of the Garnet Hill and Banning strands within the SAF system. Furthermore, new strike-slip rates on the Mission Creek strand challenge our thinking about this strand of the SAF. Recent slip rates of ~20 mm/yr (Blisniuk et al., 2013) are higher than previous estimates (Fumal et al, 2002), and higher than rates from crustal deformation models (Cooke and Dair, 2011; Fattaruso et al., 2013). Furthermore, new evidence points to a northeast dip to the Coachella Valley segment of the SAF (Fuis et al. 2012; Lindsey and Fialko, 2013). Changing the dip of the Coachella Valley segment of the SAF from vertical to northeast dipping alters the partitioning of slip amongst the strands north of the trifurcation (Fattaruso et al., 2013). The sensitivity of deformation to active fault geometry in the northern Coachella Valley is striking and highlights the need for more data gathering.